Thick film circuit assemblies may include numerous components which must be accurately positioned with respect to a thick film circuit board during manufacture. Manufacture may also require several separate sequential assembly actions that require intermediate repositioning of one or more pieces of the assembly. Each such assembly step requires time and allows for an error in assembly. It would be desirable to have a thick film circuit housing assembly design which facilitated proper alignment and assembly.
Thick film circuit boards may contain components, such as a pressure sensor, which require a housing to isolate the pressure to be measured from the ambient pressure. Such housings typically have had numerous structural components and seals to provide the desired pressure isolation.
Referring to prior art FIGS. 1 and 2, a housing assembly 110 includes a metal ring 111 which is printed on a thick film circuit board 112 and receives a flange 113 of a generally cylindrical housing 114, flange 113 being soldered to printed metal ring 111. A rubber gasket 15 is positioned in the upper opening of cylindrical housing 114 and a tube 16 is positioned in the center of gasket 15. Tube 16 is typically a polymer, and gasket 15 is typically a nitride rubber material. Housing 114 can be tin plated steel.
Manufacturing processes to fabricate such a structure typically include solder reflow and cleaning bath immersion. These processes reduce the adhesion of printed metal ring 111 to thick film circuit board 112. This is undesirable since reducing the adhesion may cause a pressure leak between ring 111 and thick film circuit board 112 and thereby cause sensor failure or reduce sensor accuracy. The adhesion is reduced because of heat retained in tin plated steel housing 114 for an extended period of time during solder reflow and during cleaning bath immersion operations.
It would be desirable to have a relatively simple and quickly assembled housing which provides a reliable pressure seal and easy assembly. These are some of the problems this invention overcomes.